Chapter 10. Copy services 493
Figure 10-3 shows the concept of FlashCopy mapping.
Figure 10-3 FlashCopy mapping
10.3.2 Multiple Target FlashCopy
The IBM Storwize V5000 Gen2 system supports up to 256 target volumes from a single
source volume. Each copy is managed by a unique mapping. Figure 10-4 shows the Multiple
Target FlashCopy implementation.
Figure 10-4 Multiple Target FlashCopy implementation
Figure 10-4 also shows four targets and mappings that are taken from a single source, along
with their interdependencies. In this example, Target 1 is the oldest (as measured from the
time that it was started) through to Target 4, which is the newest. The ordering is important
because of how the data is copied when multiple target volumes are defined and because of
the dependency chain that results.
A write to the source volume does not cause its data to be copied to all of the targets. Instead,
it is copied to the newest target volume only (Target 4 in Figure 10-4). The older targets refer
to new targets first before referring to the source.
From the point of view of an intermediate target disk (not the oldest or the newest), it treats
the set of newer target volumes and the true source volume as a type of composite source. It
treats all older volumes as a kind of target (and behaves like a source to them).
If the mapping for an intermediate target volume shows 100% progress, its target volume
contains a complete set of data. In this case, mappings treat the set of newer target volumes
(up to and including the 100% progress target) as a form of composite source.
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